Not all social media platforms are created equal.
Once you have spent time understanding the audience you are trying to reach and have created your "Audience Profile", you can now determine the social media platforms that will best reach them.
Here are some examples:
If the group you are trying to reach is in the age range of a college student that lives on a university campus, you might want to look at focusing your efforts on social platforms such as Snapchat or Instagram. You'll need to make sure your content is video and image-rich -- having a designer on hand is recommended.
Let's say you're reaching a more mature group with solid careers and larger families, you may need to consider utilizing social platforms such as LinkedIn, Facebook, and Twitter. These can be image and video rich but are small snippets that don't take a lot of time to review.
Once, your platforms have been established, now you're ready to shape your message.